Print head parking or maintenance unit for powder bed-based 3D printing, 3D printing systems and methods thereof

ABSTRACT

The invention relates to a method and a device for parking or maintaining a print head, such as a print head used for layer-by-layer manufacture of shaped parts. The print head applies a binder during the manufacture and requires parking or maintenance.

CLAIM OF PRIORITY

The present application is a continuation of U.S. patent applicationSer. No. 16/344,666 filed on Apr. 24, 2019, which is a national phase ofInternational (PCT) Patent Application PCT/DE2017/000375 filed on Nov.8, 2017 and claims priority to German Patent Application DE 10 2016 013610.3 on Nov. 15, 2016. This application claims priority to U.S. patentapplication Ser. No. 16/344,666, International Patent ApplicationPCT/DE2017/000375, and German Patent Application Number DE 10 2016 013610.3, and incorporates each by reference in its entirety.

FIELD OF THE INVENTION

The invention relates to a unit for maintenance or parking of a printhead, to devices and systems including the unit, and to methods forparking or maintaining a print head.

BACKGROUND

European Patent EP 0 431 924 B1 describes a process for producingthree-dimensional objects based on computer data. In the process, a thinlayer of particulate material is deposited on a platform and has abinder material selectively printed thereon by means of a print head.The particulate region with the binder printed thereon bonds andsolidifies under the influence of the binder and, optionally, anadditional hardener. Next, the platform is lowered by one layerthickness into a construction cylinder and provided with a new layer ofparticulate material, the latter also being printed on as describedabove. These steps are repeated until a certain desired height of theobject is achieved. Thus, the printed and solidified regions form athree-dimensional object.

Upon completion, the object made of solidified particulate material isembedded in loose particulate material, from which it is subsequentlyfreed. For this purpose a suction device may be used, for example. Thisleaves the desired objects which then have to be freed from any powderadhering to them, e.g. by brushing them off manually.

3D printing on the basis of pulverulent materials and introduction ofliquid binders is the quickest method among the layer constructiontechniques. This method allows the processing of different particulatematerials, including—as a non-exhaustive example—natural biological rawmaterials, polymeric plastic materials, metals, ceramics and sands.

In the above-mentioned method, the print head constitutes a centralelement of the device and method. The reliability of the machinecorrelates directly with the reliability of droplet generation.

In order to achieve high performance in the process, the print head ismade up of a plurality of nozzles. Said nozzles are microtechnicalactuators capable of accelerating the fluid in single droplets in thedirection of the construction field.

In the print heads of the prior art, the function of generating dropletsis achieved by piezo elements. Said piezo elements are arranged around apump chamber and, when stimulated by an electrical signal, may suddenlychange the volume of this exact chamber. The chamber is usually filledwith liquid and in communication with a nozzle channel and a nozzle. Thesudden change in volume allows a droplet to be ejected through saidnozzle.

The described microtechnical arrangement is very sensitive todisturbance. For example, air in the pump chamber drastically impairsits function. Minimal quantities of air prevent droplets from beingejected. The system also responds sensitively to soiling. Such soiling,if located in the channels, may prevent droplets forming or have anegative impact on the trajectory of the droplet.

In order to ensure the droplet-forming function, the prior art resortsto various measures during and after the actual printing: Beforeprinting, the print head is purged so as to expel any air that may bepresent in the pump chambers. After this, it is generally useful toclean the print head. The cleaning serves, on the one hand, to removethe droplets attached to the print head. Secondly, cleaning with contactallows to remove any particles or other adhesions. This is generallyfollowed by what is called spitting. Spitting corresponds to the actualprinting operation, but not yet in the product area, so that anycleaning fluid which may have gotten onto the print head by the cleaningoperation does not have an effect on the production of components by 3Dprinting.

Capping is another important function. This function protects the printhead from drying out and ingress of foreign materials before and afterthe actual printing process.

According to the prior art, a plurality of device parts are arranged forthis function in different locations on the machine. Each device parthas technical subfunction parts which protect the respective functionagainst damage from the outside. Usually, moving parts are present whichare controlled via actuators.

All individual elements of the print head maintenance unit aresusceptible to soiling and malfunction.

Therefore, it is an object of the present invention to provide a deviceand a method which are less susceptible or not susceptible at all tosoiling, adhesions and contamination, or to avoid, at least partly orentirely, the disadvantages of the prior art. Another object of thepresent invention is to provide a simpler maintenance unit for printheads or to at least simplify the disadvantages of the known differentmaintenance and capping stations.

BRIEF SUMMARY OF THE INVENTION

The above objects are achieved by a method and a device for protectingthe print head in layered construction by means of the binder jettingprocess, wherein a plurality of elements required to maintain the printhead function act and are accommodated in a space partly sealed by a gapseal. The device will be referred to hereinafter as an integratedmaintenance unit.

Said space is limited by a wall with a trough-like shape. The upper edgeof the trough is located at a certain distance from the print head. Theprint head can be positioned in the effective area of the integratedmaintenance unit by cartesian movements, without having to move thetrough.

EMBODIMENTS AND ASPECTS OF THE INVENTION

Several terms according to the invention will be explained in moredetail below.

In the sense of the invention, “3D printing methods” are all methodsknown from the prior art which enable the construction of parts inthree-dimensional molds and are compatible with the described processcomponents and devices.

“Selective binder application” or “selective binder system application”in the sense of the invention may be effected after each particulatematerial application or irregularly, i.e. non-linearly and parallelafter each particulate material application, depending on therequirements for the molded article and for optimisation of the moldedarticle production. Thus, “selective binder application” or “selectivebinder system application” may preferably be adjusted individually,during the course of the molded article production.

A “molded article” or “part” in the sense of the invention meansthree-dimensional objects manufactured by means of the method accordingto the invention or/and the device according to the invention andexhibiting dimensional stability.

The “device” used for carrying out the method according to the inventionmay be any known 3D-printing device which includes the required parts.Common components include coater, construction field, means for movingthe construction field or other parts, a metering device and heatingmeans, UV lamps and other parts which are known to the person skilled inthe art and will therefore not be described in detail herein.

The “particle materials” of use herein may be any materials known forpowder-based 3D printing, in particular sands, ceramic powders, metalpowders, plastic materials, wood particles, fibre materials, cellulosesor/and lactose powders. The particulate material is preferably afree-flowing powder when dry, but a cohesive, cut-resistant powder mayalso be used.

The “construction space” is the geometric location where the particulatematerial bed grows during the construction process by repeated coatingwith particulate material. The construction space is generally boundedby a bottom, i.e. the construction platform, by walls and an open topsurface, i.e. the construction plane.

“IR heating” as used herein means irradiation of the construction fieldby an IR radiator. The radiator may be either static or movable over theconstruction field by a displacement unit. The terms drying andhardening are not meant to be synonymous.

“Drying” means the loss of a certain volume of water. Such drying is theresult of humidity being released to the ambient air. Drying is linkedwith hardening.

“Hardening” refers to an increase in the strength of a part. In waterglass-based systems, hardening may occur by drying or chemicalhardening.

“Dissolution” means the process of a formerly solid constituent passinginto solution by the use of a solvent-based liquid. The dissolutionprocess depends on various factors. These include exposure time,temperature, the relative quantity of solvent and the type of solidused.

A “print head” in the sense of the invention means a device part whichhas a surface turned towards the construction field that includes micronozzles by which droplets can be selectively discharged onto theconstruction field. The nozzles are arranged in an area of said surfacewhich is at a certain distance from the edge of the surface. Saidsurface is substantially impervious to vapors or liquids or only hasminor gaps. Also, the print head may be substantially impervious abovesaid surface.

“Nozzle” refers to an opening in the print head from which droplets canbe selectively discharged. A nozzle is generally very small. In themethod and device of the invention, nozzles with a diameter of 10-300 μmare considered.

“Meniscus” refers to the liquid level in a nozzle in standby mode. It isdefined by a certain negative pressure in the fluid system and thesurface tension of the liquid.

An “air pocket” means air entrapped in the fluid system near the nozzle.Such an air pocket may form e.g. by evaporation of fluid. In the area ofsaid air pocket, binder or constituents of the fluid may solidify orcorrosion may be promoted by admission of air.

“Capping” in the sense of the invention is a function which protects theprint head from changing during “non-use”. In most cases, capping servesto prevent the binder from drying out and to keep the print headfunctional until its next printing operation.

A “seal” in the sense of the invention is a contacting element whichprevents the exchange of air between the environment and the cappingsponge.

Herein, a “prop” means a movable element which can be moved towards theprint head from below.

A “sponge” or “capping sponge” in the sense of the invention is anopen-pore structure that can bind fluid. In this case, the fluid isretained in the sponge by a capillary effect. In the prior art, a spongeis pressed against the print head.

According to the invention, a contactless seal (gap seal) prevents theprint head drying out during capping. A “seal gap” reduces the exchangeof steam between the chambers of the system. In this case, a gap isconsidered to be a distance of less than 5 mm between two structures.

An “anti-spill element” is understood to be a cover arranged near theliquid level to prevent large quantities of liquid level starting tomove upon stimulation and potentially reaching sensitive parts of theprint head, such as the electronic system.

An “overflow siphon” is a pipe installed in the capping trough. Forexample, it protrudes into the liquid from below. Any liquid above thelevel of the overflow siphon will drain through the siphon. This resultsin the fluid level regulating itself, at least above the siphon.

A “wiping lip” in the sense of the invention is a passive wipingelement, and when the print head touches it while passing over it, anyliquid at the lower end of the print head is pushed up, thus wiping theprint head dry and optionally also removing any dirt.

The “spitting structure” is an element adapted to catch any free-flyingdroplets generated by the print head, before they can follow air flowsin the 3D printing device as an aerosol in an uncontrolled manner.

The invention further relates to the following aspects and preferredembodiments.

In one aspect, the invention relates to a maintenance and/or parkingunit (parking station) for print heads, which is characterized in thatsaid unit includes a gap seal.

In another aspect, the invention relates to a system comprising a printhead and a maintenance and/or parking unit (parking station), whereinthe print head, in its position retracted into the maintenance unit,substantially does not touch the components of the maintenance stationand includes a gap seal.

The system or the maintenance and/or parking unit may further becharacterized in that it comprises a trough which is preferably sealedand can be filled with a liquid, and which preferably comprises a liquidinlet and outlet and/or an anti-spill element or/and a spittingstructure or/and a means for removing liquid from the print head.

The system or the maintenance and/or parking unit may further becharacterized in that it comprises a first liquid connection preferablyfor a capping liquid, for feeding a liquid into the trough or/and asecond liquid connection for overflow and draining from the trough, thedrain preferably being an overflow connection.

In further embodiments, the system or the maintenance and/or parkingunit may be characterized in that the first and/or the second liquidconnection is connected to one or more flexible tubes and/or the latterare connected to catchment means, preferably one or more storage means,preferably a storage reservoir, and/or at least one of the flexibletubes is connected to a pump for filling the trough.

Furthermore, the system or the maintenance and/or parking unit may becharacterized in that the trough has a chamfer, which is preferablycircumferential or/and has an angle of 40 to 50°, preferably of 45°,or/and a length of 2 to 4 mm, preferably of 3 mm, or/and a depth of 10to 50 mm, preferably of 30 mm, or/and comprises flexible means forattachment, preferably springs or coil springs.

In a preferred embodiment, the system or the maintenance and/or parkingunit is characterized in that the unit comprises 2, 3, 4, 5, or 6flexible means, preferably coil springs.

Furthermore, the system or the maintenance and/or parking unit may becharacterized in that the unit comprises a stop, preferably an upperstop, against which the trough can be moved by the flexible means.

In preferred embodiments, the system or the maintenance and/or parkingunit may be characterized in that the stop is adjustable by adjustingmeans, preferably by means of adjusting screws, and the distance fromthe print head to the upper edge of the trough is preferably set to 0.1to 5 mm, preferably 0.4 to 1 mm, more preferably 0.5 mm.

In further embodiments, the system or the maintenance and/or parkingunit may be characterized in that the bending force or spring force ofthe flexible means is greater than the weight force of the trough filledwith liquid, preferably in that the bending force or spring force is 10to 30 N, preferably at least 20 N, greater than the weight force of thetrough filled with liquid.

In a preferred embodiment, the system or the maintenance and/or parkingunit may be characterized in that the means for removing liquid is awiping lip.

In another aspect, the invention relates to a method for cleaning printheads, wherein the steps of purging, removing excess liquid and,optionally, dirt from the print head, and spitting are carried out inone unit (maintenance unit).

Preferably, a maintenance and parking unit as described above can beused in the method.

In preferred embodiments of the method, a maintenance unit as describedabove is approached by the print head, without substantially touchingthe maintenance unit, and in a first step a purging operation is carriedout, in a second step excess liquid and, optionally, dirt are removedfrom the print head by passing over the wiping lip, and in a third stepa spitting operation is carried out, or each of these steps may becarried out independently of the other steps.

In further embodiments, the method is designed such that, after steps 1to 3 have been carried out, or after each of the steps, the print headremains in the maintenance unit or a printing process is carried out.

The invention advantageously achieves that maintenance or capping unitspreviously present in different positions in a 3D printing machine arenow combined in one single maintenance and capping unit.

This has various advantages, which contribute to simplification and costreduction in machines of this type. Likewise, a 3D printing method isalso simplified by the use of a maintenance and parking stationaccording to the invention, and the procedure includes fewer stoppositions, which saves time and may accelerate the procedure.

A further advantage of the invention results from the simplification ofa 3D printing machine in such a way that several structural andfunctional parts are combined in one unit. Furthermore, the aspects ofthe previously used individual units are simplified in construction.This not only results in cost reduction, but also reduces the need formaintenance. Furthermore, the cleaning operation becomes more reliable,and the disadvantages of known components are improved. For example,fewer mechanical elements and thus fewer moving parts are used, whichare susceptible to wear and, thus, costly. Moreover, the 3D printingmachine can now be designed in a more compact manner, which is desirablein many ways.

The inventive concept of a contactless seal has turned out to beparticularly advantageous, because it advantageously avoids thedisadvantages of the print head and the capping sponge coming intocontact with each other. Surprisingly, using this contactless seal alsoallows to keep the print head moist enough at rest or between twoprinting processes to maintain its functionality. Furthermore, theconcept of the invention allows binder concentrations, soiling andunreliability to be reduced or avoided altogether.

FURTHER EMBODIMENTS

The device and method according to the invention are used in a systemfor the layered construction of models using inkjet printing technology.The sequence of a manufacturing cycle according to the prior art isstructured as follows: A powder layer is applied onto a constructionplatform and then leveled. Next, the layer has a fluid printed thereonaccording to the layer data of the 3D model. A portion of the materialmay be stored for bonding the particles in the powder in the form of dryparticles. After the printing process, the construction platform islowered and the process starts anew. Selectively and in certain printingmachine constructions, the printing unit and other structures involvedin the printing process may also be raised.

These steps are repeated until the part is present completely in thepowder cake built up at the same time.

The print head includes several nozzles. Depending on its design, theremay be several 10,000. These nozzles are used to produce individualdroplets upon an electrical signal. Due to the microtechnologicalconstruction, the sequence of droplets may be very quick. According tothe prior art, a droplet generation frequency of 30 kHz and more iscommon.

The droplet generation process only works if certain boundary conditionsare adhered to.

The pump chambers in which the pressure surge for the droplet isgenerated by a piezo crystal must not contain any air. The air wouldallow itself to be compressed and thus prevent propagation of thepressure surge. So, despite the signal, no droplet would form at therespective nozzle. The air may be dissolved, for example, in the fluidand not appear until inside the pump chamber.

Soiling also interferes with the droplet generation process. It may becaused, for example, by particles from the construction process. Theymay swirl around as dust in the construction space or, for example, theymay be stirred up by the print head shooting droplets onto theconstruction field itself and may adhere to the print head. If theparticles are near the nozzle, they impair the precision of thedroplets' trajectory. If a particle is located directly in a nozzle,droplet generation is prevented completely.

Thickened or sticky fluids are also detrimental to functioning. Forexample, by evaporation of solvent in the area of the nozzle, the fluidmay thicken locally to such a degree that no more droplets can begenerated. Likewise, the fluid may thicken by evaporation to such anextent that it forms an insoluble clot in the nozzle, permanentlydamaging the latter.

In order to keep the print head from drying out, the prior art usescapping. As the English word says, a cap is placed on the print head toform an air seal or prevent evaporation of the printing liquid.

The capping usually involves a seal which is placed on the lower surfaceof the print head. For this purpose, the capping consists of a propwhich is pushed onto the print head from below. To this end, the printhead is placed in the capping position and the prop is moved towards theprint head from below. The prop may be actuated, for example, by apneumatic cylinder or a mechanical system which is triggered by themovement of the print head (see for example FIG. 5 , part a).

A capping liquid is present to prevent drying out. In many cases, saidcapping liquid is bound in the prop by a sponge. The latter is broughtinto contact with the print head in the area of the nozzles (see forexample FIG. 5 , part b.

Since the nozzles are highly sensitive to soiling, both the seal and thesponge must be free from dirt. For this purpose, the capping usuallycomprises a slider. The latter separates the sponge and the seal fromthe actual construction space of the 3D printer (see for example, FIG. 6parts a and b).

All mechanically moved components are strongly influenced by the use ofsticky binders or fluids which become sticky upon drying.

Prior art devices often have problems with stuck sliders or jammedmechanical parts. In the worst case, this may cause seals to be damagedor torn off (see for example, FIG. 7 parts a and b).

All print head maintenance functions during the process are mechanicallycomplex and susceptible to soiling resulting from the processtechnology.

According to the invention, such susceptibility to soiling, the sealcontact and the spatial expansion of the elements are to be reduced.

This is achieved by a trough-shaped device whose upper edge is locatedjust below the lower edge of the print head. According to the invention,distances of less than 5 mm, preferably less than 3 mm and particularlypreferably less than 1 mm are useful in this case.

In this way, a gap seal is formed, allowing little material from theconstruction space of the 3D printer to enter into the maintenance unitand little vapor from the maintenance unit to escape from themaintenance unit.

The gap should be as small as possible. The print head moves with itsaxial system over the trough-like maintenance unit. In the process, theprint head should not touch the upper edge of the maintenance unit. Onthe one hand, the upper edge may be soiled, on the other hand, the twomerely touching may already scratch and functionally damage the printhead.

Due to manufacturing tolerances, the gap cannot be reduced at will. Inaddition, thermal expansion or chemical swelling may alter thedimensions of device parts and thereby in turn affect the gap.Experiments have shown that a gap of 0.5 mm is particularly suitable,according to the invention, for print heads with surface area dimensionsof approximately 200×200 mm.

Such a device, if it contains a quantity of liquid, may already serve,despite its passive character, as a capping for the print head. Themedium evaporating in the trough escapes only slowly through the gap.The print head remains protected against drying out for a certain time.

The protection time can be extended substantially by providing a liquidfeed. According to the invention, an inlet may be provided in thetrough. Capping liquid may be conveyed into said inlet by a pump. Inthis case, limiting the liquid level helps to prevent the print head orthe rest of the device from being inadvertently flooded. An outlet maybe provided whose inlet edge defines the liquid level.

If any unforeseen deformation or soiling beyond the normal measureoccurs in the device, the maintenance unit and the print head maycollide despite the gap provided between them.

The effect of such a collision may be mitigated by spring-mounting themaintenance unit. So, if it collides with the print head, themaintenance unit is pushed out of the way in a downward direction. Thispush may be detected in addition and the production process may bestopped.

The above-described trough may accommodate further elements for printhead maintenance. For instance, the trough may be used directly to storethe fluid during purging of the print head. The liquid being pushedthrough the head in this process then flows out via the trough. If thefluid from the print head is suitable, it may also be used at the sametime for moistening/maintaining the atmosphere in the capping.

The cleaning function may also be integrated in the trough. In thesimplest case, a wiping lip is integrated. Said wiping lip protrudessomewhat over the upper edge of the trough. As the print head moves overthe lip, any droplets attached to the print head are removed. The liquidflows out through the outlet of the trough. In addition, liquid nozzlesmay be integrated to spray down the wiping lip after the wiping processand thereby clean it again. The wiping lip should be soft and reliablycontact the print head over the entire length.

The protrusion is less than 2 mm, preferably less than 1 mm andparticularly preferably less than 0.5 mm. The lip should be bentslightly as the print head passes over it. Ideally, the lip has arectangular cross-section, and the bending causes a line-shaped contact.Since the lip touches the print head, it protrudes to a greater orlesser extent, depending on the dimensions selected, over the upper edgeof the maintenance unit.

The device may also provide a structure which prevents the droplets ofthe spitting operation from flying around freely. Said structure isarranged in the trough and just below the nozzles. A distance of 3 mmfrom the nozzle to a surface of the structure has proved useful in thisregard. The microdroplets formed hit the surface and gather there. Thesurface should be inclined such that the quantity of liquid gathering onit runs off at some point.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 : A schematic representation of the components of a powder-based3D printer in an oblique sectional view.

FIG. 2 : A schematic drawing of a conventional 3D printing process.

FIG. 3 : An illustration of the print head during the discharge ofsingle droplets onto the substrate.

FIG. 4 : A representation of the processes within a nozzle when theprint head dries out by evaporation of liquid.

FIG. 5 : Representation of a capping principle according to the priorart.

FIG. 6 : Influences on the unprotected capping during the printingprocess/risks for the print head.

FIG. 7 : Problems arising due to the drying off of binder at acontacting seal.

FIG. 8 : Representation of the possibility to carry out a cappingwithout using a contacting seal.

FIG. 9 : Protection of the print head during collision with anincorrectly adjusted capping.

FIG. 10 : Fluid system for implementing the capping principle.

FIG. 11 : Integration of several functions into the protected,gap-sealed space.

EXEMPLARY EMBODIMENT

The example outlined below serves to explain the device and processaccording to the invention. It shall not limit the potential embodimentsof the invention.

The system or unit according to the invention may be used in devices andmethods for powder-based 3D printing. The device may be combined with adevice for powder bed-based 3D printing (see for example, FIG. 1 ).

The 3D printing device comprises a powder coater (101). Particulatematerial is applied onto a construction platform (102) and smoothed bythe powder coater (101) (FIG. 2 , part a). The particulate materialapplied may consist of diverse materials. For example, basic moldingmaterials such as sands, artificial sands and ceramic particles may beused. The flow properties of these materials may differ considerably.Various coating techniques allow the forming of layers from dry,free-flowing powders to cohesive, cut-resistant powders or evenliquid-based dispersions. The height of the powder layers (107) isdetermined by the construction platform (102). The construction platform(102) is lowered before application of one layer. In the next coatingprocess, the resulting volume is filled and the excess is smoothed down.The result is an almost perfectly parallel and smooth layer of a definedheight.

After a coating process, the layer is imprinted with a liquid by meansof an inkjet print head (100) FIG. 2 , part b. The print imagecorresponds to the section through the part at the current constructionheight of the device. The liquid impacts the particulate material andslowly diffuses into it. A print head during the discharge of singledroplets onto the substrate is illustrated in FIG. 3 .

A nozzle of the print head may dry out by evaporation of liquid, such asillustrated in FIG. 4 , parts a and b.

Maintenance of the print head is performed several times during theconstruction process. This may be done before or after printing orsimultaneously with another step, e.g. the coating step. Maintenanceusually consists in purging, cleaning and spitting.

After the printing of the binder, the layer may be optionally heated(FIG. 2 , part c) For this purpose, for example, an IR radiator (200)may be passed over the construction field. The radiator may be coupledwith the axis of the coating system. During heating, part of the liquidbinder evaporates.

After this heating process, the construction platform (102) is loweredby one layer thickness. The layer-forming, printing, heating andlowering steps are repeated only until the desired part (103) has beencompleted.

After the construction process, the print head is capped. This processis necessary if the 3D printer does not start a subsequent processimmediately after the construction process.

In FIG. 8 , the printer comprises a maintenance unit which forms a gapseal (800).

The maintenance unit consists of a plastic trough (802). The contour ofthe trough is milled. The upper edge of the trough has a circumferentialchamfer with an angle of 45° and a length of 3 mm. The trough (802) ismilled to a depth of 30 mm.

In FIG. 9 , the trough (802) is connected to the stationary part (901)of the printer via coil springs (900). In this case, the springs (900)push the trough (802) against an upper stop. The overall spring forceexceeds the weight force of the filled trough by 20 N. There are foursprings.

The upper stop can be adjusted via screws. This allows the trough to beprecisely adjusted with respect to the print head. The distance from theupper edge of the trough to the print head is adjusted to 0.5 mm.

In FIG. 9 , the trough has a connector (1002) for the capping liquid(801). It terminates in a flexible tube below the trough, said flexibletube being connected to a pump and a storage reservoir of the machine.

In FIG. 10 , a second connector is provided for the overflow of liquid(1001) from the trough (802). This connector also terminates in aflexible tube which has a larger diameter than the supply tube. Theoverflow connection protrudes approx. 20 mm above the bottom of thetrough. This prevents the fill level exceeding 20 mm, because otherwisethe liquid pumped in will immediately flow out again.

In FIG. 10 , a plate (1000) is mounted approx. 2 mm above the overflowconnection. Said plate constitutes the anti-spill element. It preventsfluid squirting from the trough toward the print head in a collision.

In FIG. 11 , part of the anti-spill element is a support for a wipinglip (1100). The latter is dimensioned such that it protrudes approx. 0.5mm from the lower edge of the print head. It has a thickness of 1 mm andbends out of the way when the print head passes over it. Due to itsrectangular profile, the lip wipes the print head by contacting it in aline-shaped manner.

Also mounted above the anti-spill element is the spitting structure(1101). It consists of a number of elongated holes in a plastic block.The elongated holes are chamfered at an angle of 45°. The chamfers arefunctional surfaces and their spacing correlates with the arrangement ofthe rows of nozzles of the inkjet print head. The distance from thespitting structure (1101) is approximately 1.5 mm. The distance at whicha droplet flies with respect to the chamfer is some 3 mm.

A maintenance process during a printing process is performed as follows:

The print head moves to the position of the trough (802). In this case,the rectangular base of the print head (100) is centered above therectangular surface of the trough (802).

For purging, overpressure is applied to the tank in the print head. Thenozzles (301) are now purged with a large quantity of fluid. This is toremove any air bubbles (403) potentially present in the fluid system. Anoverpressure of 0.4 bar is applied for approximately 1 second. Thispurges some 20-30 g of fluid into the trough.

The fluid flows through the spitting structure (1101) into the trough(802). If the capping is already filled, an equivalent amount of liquidflows out of the overflow connection (1001).

Next, the print head (100) is moved over the wiping lip (1100). Themovement causes any droplets still attached to the print head (100)after purging to be removed. During the movement, the lip (1100) bends,and the edge of the wiper (1100) ensures tight contact by which theprint head (100) is cleaned in a manner leaving little residue.

During the return movement, the lip (1100) cleans the print head (100)again. After cleaning, the print head is actuated. For this purpose, afew droplets are generated. Thus, the print head is already in theretracted state when it arrives at the construction field of the device.

The generated droplets (302) impact the chamfer of the spittingstructure (1101). They collect on the chamfer until their quantity islarge enough to cause one large drop consisting of many micro dropletsto slide down and drip into the trough (802).

After the spitting, the maintenance process is finished and the printhead can return to productive operation.

After the complete construction process, the print head is moved overthe maintenance device (position of trough (802)) again. Thus, the printhead is protected against drying out. Also, dust (600) cannot soil it inthe processes following now, such as removing the construction container(104) from the 3D printer.

The liquid (801) in the trough dries off over a long period of time.Experiments have shown that, using the above arrangement and water asthe capping fluid, the print head stays moist for approximately 1 weekwithout any other measures.

This time can be extended at will by pumping fluid into the trough. Inthis manner, an idle time of the printer of several weeks can be bridgedby automatic control.

LIST OF REFERENCE NUMERALS

-   -   100 print head    -   101 coater    -   102 construction platform    -   103 part    -   104 construction container    -   105 print head path    -   106 coater path    -   107 powder layers    -   108 direction of the construction platform movement    -   109 metered droplets    -   110 powder roll    -   111 construction field edge    -   112 coater gap    -   113 coater reservoir    -   200 IR radiator    -   301 nozzles    -   302 droplets    -   303 substrate/particulate material layer    -   400 pump chamber    -   401 nozzle channel    -   402 meniscus    -   403 air pocket    -   404 drying residue    -   405 corrosion attack    -   500 seal    -   501 prop    -   502 sponge    -   600 particulate material soiling    -   601 fluid soiling    -   602 capping residue    -   603 covering slider    -   700 binder soiling    -   701 torn-off seal    -   702 cured binder residue    -   800 gap seal    -   801 capping fluid/liquid    -   802 capping trough    -   803 evaporated fluid    -   900 spring    -   901 frame    -   1000 anti-spill element    -   1001 overflow siphon/outlet    -   1002 inlet    -   1100 wiping lip    -   1101 spitting structure

What is claimed is:
 1. A unit for a print head having nozzles, whereinthe unit is for maintenance of the print head, for parking of the printhead, or both, characterized in that said unit includes a stationarypart and a trough, wherein the trough is connected to the stationarypart via flexible means and the print head is positioned over the troughfor maintenance and/or parking.
 2. The unit of claim 1, wherein the unitincludes 2, 3, 4, 5, or 6 of the flexible means.
 3. The unit of claim 1,wherein the flexible means includes coil springs.
 4. The unit of claim3, wherein the unit includes 4, 5, or 6 of the flexible means.
 5. Theunit of claim 4, wherein the trough moves via the flexible means whenthe unit is contacted by the print head.
 6. The unit of claim 5, whereinthe unit is a maintenance unit.
 7. The unit of claim 6, wherein the unitincludes a spitting structure or a wiping lip.
 8. The unit of claim 6,wherein the unit includes an anti-spill element.
 9. The unit of claim 6,wherein the unit includes an inlet for filling the trough with a fluidand a drain for removing liquid.
 10. The unit of claim 9, wherein thedrain is an overflow drain.
 11. The unit of claim 5, wherein the unit isa parking unit and the trough is a capping trough.
 12. The unit of claim11, wherein the trough is filled with a capping fluid.
 13. The unit ofclaim 12, wherein a chamber formed by the parking unit and the printhead includes an evaporated fluid, wherein the evaporated fluid includesat least a portion of the capping fluid.
 14. The unit of claim 12,wherein the flexible means has an overall spring force which exceeds aweight force of the filled trough.
 15. The unit of claim 12, wherein thecapping fluid in the trough helps keep the print head moist withoutcontacting the print head.
 16. The unit of claim 5, wherein the printhead prints a fluid including a binder and the trough has a chamfer. 17.A method including a step of parking or cleaning a print head with theunit of claim
 1. 18. A system comprising: a construction space; a coaterfor applying a powder for printing a binder; a print head havingmultiple nozzles; a unit for capping of the print head; and a cover forcovering the unit and separating the unit from a construction space toprevent particulate material soiling when the print head is printing thebinder, wherein the print head, in its position retracted into the unit,substantially does not touch the components of the unit.
 19. The systemof claim 18, wherein the unit includes a stop which creates a definedgap distance between the unit and the print head, optionally wherein thedefined gap distance is 0.1 to 5 mm.
 20. A method including a step ofcapping a print head with the system of claim 18.